Motorcycles come in various shapes and sizes according to their intended use—either on or off-road. Street machines are generally either a cruiser or a sport-racer bike, each with its own geometry that determines what range of postures a driver may assume while driving. A more comfortable driver is a safer driver because being uncomfortable or unsettled on a bike brings on mental and physical fatigue much more quickly.
Cruisers are designed for long relaxing drives on fairly straight roads or highways, with the seat positioned low for a stable center of gravity. Cruising posture is popular, and understandably so, because the laid-back riding position allows greater extension of the legs. For comfort, the driver's body is upright and slightly reclined toward the rear of the motorcycle. As with all riding positions, the head and eyes are looking forward through the path of travel. The driver's arms are extended with elbows slightly bent. The leg position can be varied with the addition of accessory foot-pegs to make the cruiser even more comfortable; however, with comfort comes less control through turns. Cruiser bikes lose the ability to carve the turns, which remains the hallmark of a sport-racer motorcycle.
Sport bikes are designed for driving fast on twisty, winding roads. This type of more aggressive driving demands that the driver assume a forward crouched posture to have more control of the vehicle. The driver's head is angled in front of the body, with the head and eyes looking through the path of travel. The upper body is angled in front of the hips. The stomach lies over the fuel tank, while the back muscles and legs support the weight of the upper torso. The driver's knees are bent and held against the fuel tank, with feet resting on foot-pegs in a position behind the knees.
The sport posture positions much of the driver's weight close to the front tire; however, the driver's ability to see far down the road is reduced. In addition, the sport riding position is often cramped, which may be difficult to sustain for more than a couple of hours. Thus, driving a motorcycle on a long ride in the sport position without any real ability to shift positions or straighten one's back, neck and shoulders may cause the driver to suffer. Over long straight distances such as interstate highway riding, it is not unusual for a driver to experience neck pain, forearm numbness, back strain and other maladies induced by the forward crouched riding posture.